Device and method for determining fetal heart rate

ABSTRACT

The invention relates to determining a fetal heart rate from an ultrasonic Doppler echo signal, which comprises at least two channels, including a first channel obtained for a first depth range and a second channel obtained for a second depth range. A first heart rate is determined from the first channel (51, 53, 55) and a second heart rate is determined from the second channel (52, 54, 56). External information on the fetal heart rate and/or the maternal heart rate, extracted from an independent source (60, 61, 62) such as an ECG, is used to select one of the first heart rate and the second heart rate as the fetal heart rate to be determined. A preferred embodiment provides for elimination of double counting heart rates by cutting out unwanted signal contributions. The disclosure further provides for an adaptive signal processing and data acquisition controlled by patient related data.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§ 371 of International Application No. PCT/EP2016/071530, filed Sep. 13,2016, published as WO 2017/046070 on Mar. 23, 2017, which claims thebenefit of European Patent Application Number 15185290.2 filed Sep. 15,2015 and 16185458.3 filed Aug. 24, 2016. These applications are herebyincorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a processing device for determining a fetalheart rate from an ultrasonic Doppler echo signal, a system fordetermining a fetal heart rate, a method for determining a fetal heartrate from an ultrasonic Doppler echo signal and a software product fordetermining a fetal heart rate from an ultrasonic Doppler echo signal.

BACKGROUND OF THE INVENTION

Electronic fetal monitors or Cardio-Toco-Graphs (CTGs) devices formeasurement and visualization of normally more than one physiologicalparameter of unborn human beings and the pregnant mother. These monitorsnormally include a base unit consisting of a thermal printer and adisplay unit, and multiple sensor elements for measuring vitalparameters e.g. uterine activity of the mother and the heartbeat of thefetus. Basically two methods are used for electronic fetal heart beatmonitoring, including an external or indirect method and an internal ordirect method.

The external or indirect method employs the use of external transducersplaced on the maternal abdomen. Typically, Ultrasound Doppler (US)transducers are used in this category, where high frequency sound wavesreflect mechanical action of the fetal heart.

The internal or direct method uses a spiral electrode to convert fetalelectrocardiogram obtained from the presenting part of the unborn. Thismethod can be used only when the presenting part is accessible andidentifiable.

Both methods, the external and the internal method, have their specificadvantages and disadvantages, whereas the Ultrasound Doppler is thepreferred method by far over the world, due to the simplicity andnoninvasiveness of its application.

There is an interest in (further) improving the existing approaches inorder to allow for a consistent and reliable determination, particularlyof the fetal heart rate.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide techniques forconsistently and reliably determining fetal heart rates.

In a first aspect of the present invention, a processing device fordetermining a fetal heart rate is presented, wherein the ultrasonicDoppler echo signal comprises at least two channels, the at least twochannels including a first channel obtained for a first depth or depthrange and a second channel obtained for a second depth or depth rangedifferent from the first depth or depth range, wherein the processingunit includes a first processing section and a second processingsection, the first processing section being arranged to determine afirst heart rate from the first channel of the echo signal, and thesecond processing section being arranged to determine a second heartrate from the second channel of the echo signal, wherein the processingunit further includes an input section arranged to receive externalinformation on the fetal heart rate to be determined and/or on a heartrate other than the fetal heart rate to be determined, and a choosingsection arranged to select one of the determined first heart rate andthe determined second heart rate as the fetal heart rate to bedetermined based on the external information.

In a second aspect of the present invention, a system for determining afetal heart rate is presented, comprising, in addition to the processingdevice according to the first aspect, an ultrasonic Doppler devicearranged to transmit an ultrasonic signal and to detect an ultrasonicDoppler echo signal and an additional heart rate determining devicearranged to determine an additional heart rate independently from thedetected ultrasonic Doppler echo signal, the additional heart rate beingthe fetal heart rate to be determined and/or on a heart rate other thanthe fetal heart rate to be determined, wherein input section of theprocessing device is arranged to receive the external information fromthe additional heart rate determining device.

In a third aspect of the present invention, a method for determining afetal heart rate is presented, wherein the ultrasonic Doppler echosignal comprises at least two channels, the at least two channelsincluding a first channel obtained for a first depth or depth range anda second channel obtained for a second depth or depth range differentfrom the first depth or depth range, the method further comprises achannel heart rate determining step of determining a first heart ratefrom the first channel of the echo signal and of determining a secondheart rate from the second channel of the echo signal, an input step ofreceiving external information on the fetal heart rate to be determinedand/or on a heart rate other than the fetal heart rate to be determined,and a choosing step of to choose one of the determined first heart rateand the determined second heart rate as the fetal heart rate to bedetermined based on the external information.

In order to cover a wide variance of maternal body sizes and fetalpresentation a wide depth range of the ultrasound beam is normallypreferable. Known ultrasound Doppler (US) transducers of devices formeasurement and visualization of fetal heart rates utilize an unfocused,approximately cylindrical ultrasound beam field. The extension of thevolume of sensitivity is determined by a characteristic time window(receive window), during which the US transducer is susceptible forreceiving the reflected signals. Typically the duration of the receivewindow is designed to cover a wide depth range of approximately 5 to 23cm. Measurements have shown, that the fetal heart is in average locatedin a distance of 6 to 10 cm from the surface of the transducer. In orderto cover a wide variety of body sizes a great depth range is desirable.It is to be realized, however, that transducers utilizing the Dopplerprinciple are susceptible to frequency shifts caused by all movingstructures inside the volume of sensitivity. The signal containing theinformation of the fetal heart in many cases represents only a smallportion of the entire received signal. Signal contributions from othermoving structures, like maternal arteries lying behind the fetal heartare frequently superimposed. The signal strength of the unwantedinterference signal is influenced by various factors and changes overtime. One major factor for influencing the signal strength ratio betweenfetal and maternal signal are medications. Some tocolytics, for example,are known to increase the signal strength of the maternal heart beat,often dramatically. For selecting the correct heart rate out of amixture of different superimposed heart rate values the signal strengthand the heart rate value itself plays an important role. Fetal heartrate values are normally expected to be between 120 and 160 bpm, whereasthe maternal heart rate under normal conditions is far below 100 bpm.Medication and the stress during birth may force, however, the maternalpulse easily up to 160 bpm. Under these conditions conventionalalgorithms for selecting the correct fetal heart rate may be misguidedto select the maternal heart rate instead of the fetal heart rate.Measuring wrong heart rates especially during the second stage of laboris actually a widespread phenomenon. Heart rate alterations caused bymaternal and fetal signal interaction are retrospectively difficult toidentify and may at worst lead to a misinterpretation.

The first to third aspects of the present invention are particularlyaimed at supporting a decision and selection algorithm, which selectsexactly the fetal heart rate out of the plurality of heart rates. Thismay be done by comparing (all) heart rate values coming from theultrasound Doppler channel with a heart rate derived from, for example,independent transducers or a built in second independent heart ratedetection channels. The independent heart rate measuring channelpreferably uses different measuring techniques e.g. light absorption,movement detection with accelerometers or electrical activity (ECG). Thesecond channel for calculating a heart rate should preferably ensurethat only a maternal heart rate can be calculated (even though theseparate channel or source may also provide the fetal heart rate forcomparison). An optical method with infrared absorption for example is avery safe and accurate way for retrieving solely the maternal heartrate. Feeding this heart rate to a decision unit of an ultrasoundDoppler signal processing algorithm allows the exclusion of a heart ratewhich is in the range of the heart rate of the second source. Thedecision and selection algorithm doing the signal scoring then maydiscard a heart rate value which has the highest scoring, but is mostlikely a maternal heart rate. In this case a second heart rate valuewith lower scoring most likely will be the fetal heart rate. If thisheart rate has a sufficient scoring and quality the algorithm may outputthis.

In a preferred embodiment, the additional heart rate determining deviceincludes one or more of an accelerometer unit arranged to measurematernal heart movements, an electrocardiography unit arranged tomeasure maternal electrocardiography activity, a light sensor unitarranged to measure light absorption indicative of pulsating maternaloxygen saturation, a blood pressure sensor arranged to measure maternalblood pressure, and an additional ultrasonic Doppler unit arranged todetermine a heart rate other than the fetal heart rate to be determined.

For the independent heart rate source (additional heart rate determiningdevice), more than one independent source is thinkable. ECG, movementand infrared sensors are easily capable of being integrated into theultrasound Doppler sensor unit, thus providing more than one source fora maternal heart rate. In addition, the independent maternal heart ratesource needs not necessarily be a physical part of the ultrasoundsensor. The maternal heart rate values can also be provided by messagetransmission to the ultrasound signal processing unit from a completelydifferent device for instance from a blood pressure unit. It is also notnecessary to provide the maternal heart rate value continuously or asbeat to beat values. Spot check values with a fixed or adjustingrepetition period should be completely adequate for this purpose, atleast as long the depth distribution of the ultrasound Doppler signalsources is not subject of sudden changes.

It is noted that the more independent sources for the maternal heartrate are available, the more reliable is the decision to excludeunwanted heart rates.

In one embodiment a ultrasound transducer with built in two or moreprocessing channels for depth segmentation of the ultrasound Dopplersignal contains one or more channels for detecting the maternal heartrate independently. Possible sources could be for example anaccelerometer for measuring the pulsating movements caused by thematernal heart, ECG electrodes on the bottom of the transducer housing,which are in direct contact with the maternal skin for measuring the ECGactivity or a light sensor for measuring the light absorption caused bypulsating oxygen saturation.

The heart rate values provided by depth segment signal processingchannels are compared against the value provided from the independentchannel. When selecting a heart rate channel the selection algorithm canthen exclude the depth segment which roughly has a heart rate of theindependent channel.

In another embodiment, an ultrasound transducer allows message transferof heart rate values from an external source. Here, the ultrasoundtransducer with built in two or more processing channels for depthsegmentation of the ultrasound Doppler signal is able to receivemessages over wired or wireless communication channels from a secondtransducer (or other source). The second transducer may contain meansfor an independent determination of one or more heart rates of a knownsource. For instance a Toco transducer may include an ECG signalprocessing path. With maternal ECG electrodes attached, the heart rateof this channel is clearly maternal. If a valid heart rate value isavailable, a message is sent from this transducer as a broadcast to allconnected ultrasound transducers. All ultrasound transducers connectedto this system can use this information to exclude the depth segmenthaving roughly the value of the message.

In addition or in alternative to the sources listed already above, assources for independent heart rate values also a heart rate derived fromthe noninvasive blood pressure measurement, a pulse rate from a SpO2sensor are contemplated.

When measuring the heart rates of twins or triplets two or moreultrasound transducers are normally in use. Depending of theirplacement, each transducer may have one or more valid fetal heart ratesin different depth segments. In order to prevent the transducers toselect all the same depth segment, each ultrasound transducer maycommunicate by broadcast messages the heart rate value and/or the depthrange/segment to the other transducers. Depending on a defined priority,a transducer with lower priority can exclude a depth segment which isalready selected by a transducer with higher priority. In a particularcase a second ultrasound transducer placed over the maternal heart maybe used to exclude the depth segment containing the maternal heart rateof the first transducer.

Furthermore, as discussed above, multiple ultrasound transducers mayreceive broadcast messages with heart rate values from known independentsources to exclude heart rate values of the depth segments havingroughly the same value.

In a preferred embodiment of the invention, the processing devicecomprises a first demodulation unit arranged to demodulate the echosignal using first channel selection information and a first inputfrequency based on the carrier frequency of the ultrasonic signal usedfor generating the echo signal as the demodulation frequency, thusproviding a first demodulated signal, and a second demodulation unitarranged to demodulate the echo signal using second channel selectioninformation and a second input frequency based on the carrier frequencyof the ultrasonic signal used for generating the echo signal as thedemodulation frequency, thus providing a second demodulated signal,wherein the processing device is arranged to selectively operate in oneof a channel mode and a phase shift mode, wherein, in the channel mode,the first channel selection information indicates the first channel, thesecond channel information indicates the second channel and the firstand second input frequency are identical, and wherein, in thephase-shift mode, the first channel selection information and the secondchannel selection information indicate the same channel, wherein thereis a shift of 90 degrees in phase between the first and the second inputfrequency, and the first demodulation unit and the second demodulationunit function, respectively, as the reference demodulation unit and thephase shift demodulation unit, such that the comparison unit is arrangedto compare the first and second demodulated signal so to obtain theinformation on the time-wise relation, wherein the processing device isarranged to switch from the channel mode to the phase-shift mode inaccordance with a selection of the choosing section, such that thechannel indicated by the first and second channel information is thechannel providing the determined heart rate selected as the fetal heartrate.

In this embodiment, there are provided two distinct modes, one of whichis directed to addressing the separate channels, so that, based onexternal heart rate information, the proper channel for the fetal heartbeat can be determined by means of parallel processing chains. Once thechannel is determined, i.e. where the other channel (or at least one ofthe other channels) is found as not providing (the best) information onthe fetal heart beat, the processing chain previously used for this“discarded” channel is switched to the phase-shifted processing asdiscussed below with respect to the fourth to sixth aspect. In otherwords, here the processing chains are used for different purposesdepending on the mode of the processing device in total.

In specific implementations, the embodiment may provide for individuallyconfigurable signal processing channels controlled by patient data forpatient constitution dependent signal processing control, paralleloperation of multiple channels using different configurations formeasuring multiple sources with one ultrasound transducer (for exampletwins+mother) and a switchable demodulation method for doubling freeheart rate registration.

Particularly, a multiple use of ultrasound Doppler demodulation channelsmay provide at least some of the following advantages: allowing forsegmentations of the volume of sensitivity to increase signal to noiseratio, avoiding double counting if quadrature demodulation is applied,putting aside channels with different evaluation rule sets allowsadditional background calculations yielding in higher accuracy, parallelheart rate calculation with different rule sets increases the confidencelevel for measuring the correct heart rate, allowing of a measuring ofmultiple sources with one transducer (for example twins+mother).

In a fourth aspect of the present invention, a processing device fordetermining a fetal heart rate from an ultrasonic Doppler echo signal ispresented, comprising a reference demodulation unit arranged todemodulate the echo signal using a carrier frequency of the ultrasonicsignal used for generating the echo signal as a demodulation frequency,thus providing a reference demodulated signal, a phase shiftdemodulation unit arranged to demodulate the echo signal using thedemodulation frequency shifted by 90 degrees in comparison to thereference demodulation unit, thus providing a phase shift demodulatedsignal, a comparison unit arranged to compare the reference demodulatedsignal and the phase shift demodulated signal so to obtain informationon a time-wise relation between corresponding respective signal pointsof the reference demodulated signal and the phase shift demodulatedsignal, and a processing unit arranged to process the information on thetime-wise relation so to determine timing information indicative offirst portions of the echo signal corresponding to a movement in a firstdirection and of second portions of the echo signal corresponding to amovement in a second direction opposite to the first direction, whereinthe processing unit is further arranged to use the timing information ina process of determining the fetal heart rate.

In a fifth aspect of the present invention, a system for determining afetal heart rate is presented, comprising an ultrasonic Doppler devicearranged to transmit an ultrasonic signal and to detect an ultrasonicDoppler echo signal, the processing device according to the fourthaspect coupled to the ultrasonic Doppler device for receiving thedetected ultrasonic Doppler echo signal.

In a sixth aspect of the present invention, a method for determining afetal heart rate from an ultrasonic Doppler echo signal is presented,comprising a reference demodulation step of demodulating the echo signalusing a carrier frequency of the ultrasonic signal used for generatingthe echo signal as a demodulation frequency, thus providing a referencedemodulated signal, a phase shift demodulation step of demodulating theecho signal using the demodulation frequency shifted by 90 degrees incomparison to the reference demodulation step, thus providing a phaseshift demodulated signal, a comparison step of comparing the referencedemodulated signal and the phase shift demodulated signal so to obtaininformation on a time-wise relation between corresponding respectivesignal points of the reference demodulated signal and the phase shiftdemodulated signal, and a processing step of processing the informationon the time-wise relation so to determine timing information indicativeof first portions of the echo signal corresponding to a movement in afirst direction and of second portions of the echo signal correspondingto a movement in a second direction opposite to the first direction,wherein the processing step includes using the timing information in aprocess of determining the fetal heart rate.

In the context of employing the Doppler effect using ultrasound, anincoming Doppler signal (i.e. the echo) is typically extracted from thecarrier by means of a synchronous demodulation. This approach is quitesimple and does not require high technical effort.

In the context of these aspects of the present invention, it wasrealized by the inventors that this method has one important drawback,since demodulation is done with the same frequency as the carrier, thedirection information respectively sign of the Doppler shift is lostirreversibly.

If this technique is applied for heart beat detection a differentiationbetween a systolic heart activity and a diastolic heart activity is nolonger possible. Both activities appear as two peaks in the timediagram. Under normal conditions the time t1 between systolic anddiastolic heart action is significantly lower than the time t2 betweenthe diastole and the systole of the following heart action (see, forexample, FIG. 2). The input signal shows two activity peaks, onerepresenting the heart contraction (systole), and the other representingthe heart relaxation (diastole). Given the normal framework, accordingto the Doppler principle systole causes a negative frequency shift anddiastole a positive. Since the sign is lost during demodulation theactually unwanted first or second peak of the heart activity can not beidentified or eliminated, thus creating unwanted peaks of theautocorrelation function at a higher frequency.

As it becomes clear from the above as well as from the furtherdiscussion provided herein, conventional signal processing forultrasonic Doppler echoes has difficulties in selecting the correctheart rate when the time ratio between two subsequent heart activitiesreaches one. A straightforward approach from the general theory ofsignal processing for eliminating doubling could be to remove theunwanted signal components of the heart activity, either systole ordiastole. An example of such simple method would be to put the values ofthe incoming data stream to zero for a defined time after detection of aheart activity. In practice, however, the recorded echo signals are soweak and hidden in the noise that a peak trigger method as used forexample to evaluate an ECG signal is not possible. Motion artifactscaused by mother or child produce strong signal fluctuations which makethe use of an autocorrelation mandatory. A further possibility tocompensate for the loss of movement direction could be to use ademodulation frequency which is higher than the transmission frequency.Suitable filters could then, for example, remove the unwanted frequencycomponents, for example, during diastole. The inventors realized that atechnically less demanding and complex solution may be found by using amethod like quadrature demodulation. For such quadrature demodulation,the received signal is demodulated with the original transmissionfrequency and then in parallel with the 90 degrees phase shiftedtransmission frequency. Comparing the two signals to each other showsthat the phase-shifted signal either leads or lags the reference signal.

Information on such leading or lagging can be used for distinguishingbetween systolic and diastolic movements, wherein this may be used fordetermining the fetal heart rate as such or may be used for maskingunwanted portions of the ultrasound echo signal used for determinationof the fetal heart rate, thereby at least reducing detrimental effectsof such portions.

The signal points considered in this context are preferably zerocrossings of the signals, even though other points may be considered inthe alternative or in addition, e.g. points of maximum positive and/ornegative amplitude.

In a preferred embodiment, the processing unit is arranged toselectively cut out portions of a demodulated signal obtained bydemodulating the echo signal based on the timing information, so toobtain a cut out demodulated signal, wherein the processing unit isfurther arranged to determine the fetal heart rate using the cut outdemodulated signal by means of autocorrelation.

The timing information, eventually including information about the phaseof the heart movement, may be used to remove or disregard portions ofthe ultrasonic Doppler echo signal, thereby allowing for avoidingundesired artifacts. In particular, by cutting out either the systolicor the diastolic heart activity, a doubling is avoided in theautocorrelation.

In a preferred embodiment, the processing unit is further arranged todetermine an uncut heart rate by subjecting the reference demodulatedsignal to autocorrelation and to determine a cut heart rate bysubjecting the cut out demodulated signal to autocorrelation, whereinthe processing unit further includes a selection section arranged todetermine the fetal heart rate by selecting one of the uncut heart rateand the cut heart rate.

It was further found by the inventors that a loss in beat to beataccuracy which might potentially be caused by removing information bymeans of the cutting out, a heart rate may be determined in parallel byconventional means (e.g. applying autocorrelation on the un-cut orcomplete ultrasonic Doppler echo signal), while the a comparison of theheart rate obtained from the cut out demodulated signal with aconventionally obtained heart rate may be used for avoiding incorrectlyconsidering the doubled heart rate.

In a preferred embodiment, the processing unit is arranged to subjectthe timing information to autocorrelation so to obtain the fetal heartrate.

It is possible to use, for example, a stream of signs forming the timinginformation, to calculate the heart rate by use of an autocorrelation.Either the positive sign or the negative sign or both might be used forcorrelation. Also possible is the independent evaluation of positive andnegative signs.

In a mix of features of the above embodiments, a phase considerationheart rate may be obtained from the timing information by means ofautocorrelation, wherein this phase consideration heart rate is usedtogether with a conventionally obtained heart rate to avoid confusioncaused by doubled heart rated.

The fourth to sixth aspect of the present invention as discussed aboveand as discussed with respect to exemplary embodiments referring to thefigures are provided in the context of the first to third aspect of thepresent invention, respectively.

In a seventh aspect of the present invention, a processing device fordetermining a fetal heart rate is presented, wherein the processing unitis arranged to receive patient related data, the processing unit isprovided with setting data relevant to the processing provided by theprocessing unit, and the processing unit is arranged to adjust thesetting data based on the received patient related data.

In an eighth aspect of the present invention, a system for determining afetal heart rate is presented, the system comprising an ultrasonicDoppler device arranged to transmit an ultrasonic signal and to detectan ultrasonic Doppler echo signal, and the processing device accordingto the seventh aspect of the invention coupled to the ultrasonic Dopplerdevice for receiving the detected ultrasonic Doppler echo signal,wherein the ultrasonic Doppler device is arranged to receive patientrelated data, the ultrasonic Doppler device is provided with settingdata relevant to its operation, and the ultrasonic Doppler device isarranged to adjust the setting data based on the received patientrelated data.

In a ninth aspect of the present invention, a method for determining afetal heart rate is presented, the method comprising a receiving step ofreceiving patient related data, and an adjustment step of adjusting thesetting data relevant to the operation of the method based on thereceived patient related data.

Especially when used in hospitals, monitors or device for measurementand visualization of physiological parameters like fetal heart beat areconnected to a local network infrastructure which connects the monitorwith a frequently centralized visualization and archiving program. Thisprogram basically is a data base containing all relevant patient datacollected over time. CTG trace recordings taken at different times ofthe pregnancy, medications, anamnesis, patient data and many otherphysiological parameters are stored and documented in the electronichealth record.

Currently, such connected fetal monitors primarily use the electronichealth record data base for archiving and storing the data recorded withthe applied sensors. Some of the monitors provide special procedures,where a pregnant woman is admitted respectively discharged to a certainlabor and delivery room or monitor. After the admit/discharge procedure,the monitor is connected with the data base containing the personalinformation of the patient. Conventionally, the fetal monitor mainlyuses the data base only for dumping the measurement data. Readinginformation out of the data base to the monitor is only fragmentarilyused.

Monitoring the fetal and maternal physiological parameters require verysensitive sensor elements for picking up weak and noisy signals. Thelevel of sensitivity is normally fixed and defined by the experience ofthe manufacturer to cover a broad range of body constitutions. With theincreasing number of overweighed patients obtaining signals withsuitable strength is more and more difficult. Simply raising the levelof sensitivity for all is not a good way to cover the upper end of theweight scale, because the likelihood of recording unwanted signalsincreases also. For sensor systems using ultrasound, electric ormagnetic fields raising the field strength is also problematic, since insuch case normal weighted or underweighted patients would be exposed tounnecessarily high field strength. Furthermore the operating time ofbattery operated equipment would be reduced unnecessarily. Fetalmonitors already offer some simple possibilities of manual adjustments.For example the sensitivity of a Toco sensor can be reduced by 50% inorder to avoid clipping of the recording if the sensor is applied toslim women. Adjustment of sensitivity or field energy requires a manualinteraction of an operator. Manual interactions are always timeconsuming and require deep knowledge about the method of operation.Adding additional possibilities of setting adjustment is, on the onehand desirable, but on the other hand it confuses the operator andincreases the time for instrument set-up. Reducing the time forinstrument preparation and set-up is not unimportant, because in manycountries the hospital personnel is reduced, due to economic pressure.Furthermore, all setting changes have to be stored in a memory forrecovery after an unexpected power loss. If the monitor does not providea mechanism for return to the default setting after a patient change,there is a risk of monitoring a new patient with inappropriate settings.

The inventors realized that especially fat has an extremely negativeinfluence on the measurability of all physiological parameters measuredduring labor and delivery. For adults, overweight and obesity ranges aredetermined by using weight and height to calculate a number called the“body mass index” (BMI). BMI is used because, for most people, itcorrelates with their amount of body fat. Patient weight and height, aswell as week of gestation are essential parts of the electronic healthrecord. By combining this information, a classification in, for instancethree categories fat, normal and slim is easily possible. With this BMIcoupled classification, all sensors or transducers connected to a fetalmonitoring system can be forced to the point of their optimumperformance. The gist of this approach is automating the settingadjustment for each physiological parameter by use of bodyclassification categories. The classification categories may be obtainedby, for example, automatic read of relevant data out of the patienthealth record at the time of admittance, manual entry at the monitor bytouch screen or keyboard at the time of admittance, data entry byreading barcode tags or wireless ID tags at the time of admittance.

Adjusting critical measurement settings of each physiological parameterautomatically allows for advantages in that measurement performance maybe (even significantly) increased due to optimized signal to noise,monitor set up time is reduced, the point of operation is optimized, asalso settings may be changed automatically which are not commonly knownby operators, the exposure to energy fields e.g. ultrasound is improvedand the operating time of battery powered equipment is improved.

In a preferred embodiment, wherein the processing unit is arranged to becoupled with a data base and to receive the patient related data fromthe data base, provided with a reading section arranged for reading outa data carrier in which patient related data is stored, and/or providedwith an interface section which is arranged to allow for an input ofpatient related data by a user of the processing device.

The seventh to ninth aspect of the present invention as discussed aboveand as discussed with respect to exemplary embodiments referring to thefigures are preferably provided in the context of the first to thirdaspect and/or the fourth to sixth aspect of the present invention,respectively. Nevertheless, it is also contemplated to provide theseventh to ninth aspects and their embodiments as discussed hereinseparately, i.e. independently from the first to third aspect of thepresent invention, or in combination with just the fourth to sixthaspect.

In a further aspect of the present invention a computer program ispresented for determining a fetal heart rate from an ultrasonic Dopplerecho signal, the software product comprising program code means forcausing a processing device according to first, fourth or seventh aspectto carry out the steps of the method according to the third, sixth orninth aspect, respectively, when the software product is run on theprocessing device.

It shall be understood that the processing device of claim 1, the systemof claim 3, the method for determining a fetal heart rate of claim 5,and the computer program of claim 6 have similar and/or identicalpreferred embodiments, in particular, as defined in the dependentclaims.

It shall be understood that a preferred embodiment of the invention canalso be any combination of the dependent claims or above embodimentswith the respective independent claim.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following drawings:

FIG. 1 shows a number of diagrams illustrating the concept ofautocorrelation,

FIG. 2 shows an illustration of for autocorrelation of a non-equidistantsimplified heart activity,

FIG. 3 shows an illustration of for autocorrelation of an equidistantsimplified heart activity,

FIG. 4 shows an illustration of phase shifted demodulation of an(artificial) ultrasonic Doppler echo signal,

FIG. 5 shows an example of a raw chain of signs corresponding to a phaseshifted demodulation as shown in FIG. 4,

FIG. 6 shows an example of a processed chain of signs derived from theraw chain of signs illustrated in FIG. 5,

FIG. 7 shows a typical example of an expected velocity profile of aheart activity,

FIG. 8 shows a basic signal processing path for avoiding doubling inaccordance with an element of the present disclosure,

FIG. 9 allows for a comparison of a conventionally rectified andfiltered signal and a gate-controlled signal processed according to anelement of the present disclosure,

FIG. 10 shows a signal processing according to a second element of thepresent disclosure,

FIG. 11 shows a signal processing according to a third element of thepresent disclosure,

FIG. 12 shows a signal processing according to a forth element of thepresent disclosure,

FIG. 13 shows an example of a cardiotocogramm with fetal and maternalheart rate traces,

FIG. 14 shows a combined ultrasound Doppler signal resulting fromsuperposition of a fetal heart signal and a maternal heart signal,

FIG. 15 illustrates a signal processing according to an embodiment ofthe invention,

FIG. 16 schematically shows a further element of the present disclosure,

FIG. 17 schematically shows another element of the present disclosure,

FIG. 18 schematically shows a yet further element of the presentdisclosure,

FIG. 19 schematically shows a processing device in accordance withanother embodiment of the invention,

FIG. 20 shows a schematic flow diagram illustrating a method fordetermining a fetal heart rate in accordance with an embodiment of theinvention,

FIG. 21 schematically shows a processing device in accordance with yetanother embodiment of the invention in a channel mode, and

FIG. 22 schematically shows the processing device of FIG. 21 in aphase-shift mode.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a number of diagrams illustrating the concept ofautocorrelation.

Firstly, as a non-limiting introduction to the discussion of theautocorrelation, a discussion of an exemplary realization of adetermination of a fetal heart beat is given.

An ultrasound Doppler transducer is placed on the abdomen of the motherand held in place by an elastic belt fitted around the waist. TheDoppler Effect is based on the principle that sound waves reflected froma moving target are shifted in frequency depending on the direction andspeed of movement. Based on this principle, mechanical contractions ofthe fetal heart muscle lead to periodic signal patterns in theultrasound reflection. The periodicity of the patterns is used by fetalmonitors to determine the fetus' current heart rate. The majority offetal heart rate transducers use the pulsed-wave principle. An array ofpiezo elements is used as an electro mechanical converter. This arrayoperates bi-directional as transmitter and receiver. A sequencercontrols the timely switch over between transmit and receive phase.During the transmission phase the piezo array is repetitively excited togenerate ultrasonic wave packets which are traveling towards the fetalheart. These traveling wave packets are reflected and frequency shifteddue to the Doppler effect on moving layers in the body of the pregnantwoman, for example at the fetal heart. The received reflected signal isdemodulated by a synchronous demodulator utilizing exactly the samefrequency as used for the transmit burst. After demodulation,integration, amplification and band-pass filtering the Doppler frequencyis available for signal processing. The received weak Doppler shiftedecho signal is embedded in noise and signals from artifacts caused bybody or transducer movements.

In order to extract the periodic signal out of the noise the method ofautocorrelation is applied. Autocorrelation is a mathematical method forfinding repeating patterns, such as the presence of a periodic signalwhich has been buried under noise. The result of the correlation is afunction which allows the exact calculation of heart rate.

FIG. 1 shows a simplified illustration how the output of anautocorrelation is calculated. A signal is multiplied with the timeshifted copy of itself point wise. The result of each multiplication issummed up.

In FIG. 1, the hatched rectangles show where the product is not zero andthus contributing to the autocorrelation function.

FIG. 1a ) shows the case of a time shift 0 (τ=0), where the similaritycorresponds to the entire pulse. FIG. 1b ) shows the case of a timeshift of 128 lags (τ=128), where the similarity corresponds to the halfthe pulse (3 times over). FIG. 1c ) shows the case of a time shift of256 lags (τ=256), where there is no similarity at all. FIG. 1d ) showsthe case of a time shift of 384 lags (τ=384), where the similaritycorresponds to the half the pulse (2 times over). The result of theautocorrelation is given in FIG. 1e ), wherein the arrows point fromFIG. 1a ) to 1 d) to the corresponding portions of the result.

The abscissa of FIG. 1 shows the lapse of time (in lags), while theordinate is provided with arbitrary units.

At time shift 0 the autocorrelation result (FIG. 1e ) has its maximumrepresenting the energy of the signal. At time shift 512 (not shown inFIG. 1a ) to d)) the autocorrelation function has a first maximum(τ=512). This peak represents the first repetition of the signalsperiodicity. In taking the i-value of this peak the signal frequency canbe calculated.

FIG. 2 shows an illustration of for autocorrelation of a non-equidistantsimplified heart activity.

Typically, the incoming Doppler echo signal is extracted from thecarrier by means of synchronous demodulation, wherein this method isquite simple and does not require high technical effort. The inventorsrealized that this method has one important drawback in that, sincedemodulation is done with the same frequency as the carrier, thedirection information (respectively sign) of the Doppler shift is lostirreversibly.

If such technique is applied for heart beat detection a differentiationbetween a systolic heart activity and a diastolic heart activity is nolonger possible. Both activities appear as two peaks in the time diagram(see FIG. 2a )). Under normal conditions the time (t1) between systolicand diastolic heart action is significantly lower than the time (t2)between the diastole and the systole of the following heart action.

The input signal shows (FIG. 2a ) two activity peaks, one representingthe heart contraction (S=systole), and the other representing the heartrelaxation (D=diastole). According to the Doppler principle systolecauses a negative frequency shift and diastole a positive. Since thesign is lost during demodulation the actually unwanted first or secondpeak of the heart activity can't be eliminated, thus creating unwantedpeaks of the autocorrelation function at a higher frequency.

Given is a periodical heart beat consisting of contraction (S) andrelaxation (D) with a frequency of 2 Hz=120 bpm. The time betweensystole and diastole is 100 ms (the abscissa of FIG. 2a ) showing timein units of seconds, the ordinate being normalized). The ACF result(FIG. 2b ), with abscissa showing lags and an arbitrarily providedordinate) shows two peaks with an amplitude of 100, one at τ=200 and theother at τ=1024.

Both peaks have the same amplitude. When calculating the relatedfrequency τ=200 yields in a frequency of 614 bpm, while the second peakat τ=1024 still shows 120 bpm. In order to avoid false HR evaluation theevaluation range of the CTGs using auto correlation is limited to arange of approx. 240 (τ=512) The line L illustrates the peak examinationlimit.

Peak evaluation and peak selection is done in a second part of thesignal processing, the so called post processing. This function normallysimply cuts off peaks which have a frequency higher than 240 bpm. Thesetting of the peak examination limit has an essential effect on thedoubling behavior of the monitor. If the setting is at 240 bpm all heartrates above 120 bpm are “doubling save”, because if the heart rate isdoubled, the result is always outside the evaluation limit. Fetal heartrate traces in the great majority cover the area from 140 bpm to 180bpm, whereas the maternal heart rate is mostly below 100 bpm.

Besides the evaluation limit setting, probably the most important factorfor doubling is the ratio between t1 and t2. If the t1/t2 ratio reaches1 the heart rate value is doubled with a high likelihood. Unfortunatelythe ultrasound Doppler sensor is susceptible to all moving structuresinside the volume of sensitivity. The signal containing the informationof the fetal heart in many cases represents only a small portion of theentire received signal. Signal contributions from other movingstructures, like maternal arteries lying behind the fetal heart arefrequently superimposed especially if medications increase pulse rateand blood pressure of the mother.

The time ration t1/t2 is important for doubling. Due to the physiologyof the human heart, the time ratio t1/t2 is not constant over the heartrate range. It can be said that at heart rates between 80 bpm and 120bpm the likelihood of reaching a ratio of 1 is high. Doubling afrequency of 80 bpm is then recorded as 160 bmp. This might exactly bethe heart rate range expected for a fetus. Cases where the (doubled)heart rate of the mother was recorded over hours due to absence of afetal heart rate are reported at times.

FIG. 3 shows an illustration of for autocorrelation of an equidistantsimplified heart activity, in an arrangement similar to that of FIG. 2.

FIG. 3 in particular illustrates the effect of doubling. In the inputsignal, t1 is prolonged to approximately the same value as t2. As aresult the maximum peak (P1), which previously was outside theevaluation limit, is now exactly on the limit line and thus creating aHR value of 4 Hz=240 bpm (τ=512 yields in 4 Hz). The peak evaluationfunction has to select P1 instead of P2.

Double count is mainly observed in cases of fetal bradycardia, or whenthe maternal pulse is inadvertently measured. Normally sequences ofdouble count caused by fetal bradycardia can be easily identified and donot pose a risk for wrong trace interpretation, if the maternal heartrate is recorded with an independent heart rate measurement channel(e.g. maternal pulse measured with an infrared sensor). Nevertheless,measuring a doubled maternal heart rate inadvertently is a serious risk,because maternal heart rate patterns can mimic fetal heart ratepatterns. The doubling may remain undiscovered for a long time, becausethe common method of cross channel verification fails in detectingmultiples of a heart rate having the identical source.

FIG. 4 shows an illustration of phase shifted demodulation of an(artificial) ultrasonic Doppler echo signal.

In particular, FIG. 4 shows a reference signal (the original artificialDoppler signal) and an artificial Doppler signal demodulated with 90degrees phase shift. The first signal 1 was demodulated without phaseshift, while the second waveform 2 is demodulated with a 90 degree phaseshift. In the first half of the wave diagram, the first signal 1precedes the second signal 2 clearly. At the maximum of the signalamplitude the phasing changes abruptly, from here the second signal 2precedes the first signal 1 for three oscillations. For the rest of theoscillation the phasing switches back to the initial condition.

Depending on the point of view, the first and the tail part can be seenas a forward movement whereas the central part with the threeoscillations could be a backward movement. Measuring a time differencebetween the zero crossings of the first signal 1 and the zero crossingsof the second signal 2, respectively, result in either negative orpositive values. For reconstructing the movement direction, basicallyonly the sign without the value is of interest. Evaluating the zerocrossings of both signals 1, 2 allows for obtaining a chain of signs 3.

FIG. 5 shows an example of a raw chain of signs corresponding to a phaseshifted demodulation as shown in FIG. 4.

FIG. 5 shows a typical sequence of signs in a raw form. Noise andoverlaid inverse moving parts in the measurement area are reasons forstrong sign fluctuations as shown in FIG. 5 (the value 0 indicating thateither there was no difference between the zero crossings or the resultswas indeterminate).

FIG. 6 shows an example of a processed chain of signs derived from theraw chain of signs illustrated in FIG. 5.

Applying known and appropriate signal processing methods to the chain ofraw signs shown in FIG. 5 yields a smoothened sign signal as shown inFIG. 6, which can be used for further signal processing.

The sign shown in FIG. 6 correlates very well with the expected velocityprofile of a heart activity as shown in FIG. 7.

Bearing in mind the different scaling of the abscissa, it can be seenthat the smoothened sign signal shown in FIG. 6 represents the velocitydirection of a heart activity very well, so it can be used to cut outunwanted parts of the signal. In other words, the inventors realizedthat the binary sign values may be used to gate the reference signal.

FIG. 8 shows a basic signal processing path for avoiding doubling inaccordance with an element of the present disclosure.

This element provides for by cutting out undesired signal episodes thatare identified by their movement direction, respectively sign. Areference signal (reference demodulated signal) 10 demodulated with 0degree phase shift and a second signal (phase shift demodulated signal)15 demodulated from the same source with 90 degree phase shift are fedto respective high pass filters 20, 21 to remove DC offset. Thereference signal 10 passes the conventional signal processing chainrequired as preparation for an autocorrelation (i.e. magnitudeprocessing 22, low pass filter 23 and delay 24).

Both signals are tapped after the high pass filters 20, 21. The highpassed signals are delayed (blocks 25, 26) to compensate the smoothingfilter delay of the approximated envelope. Afterwards these signals arepassed through an envelope controlled noise gate 27, 28, respective, toavoid sign detections on plain noise signals e.g. during mechanicalpause periods. The next stage for both signals is a respective zerocrossing detector 29, 30. By comparing the timely relationship of thetwo outputs of the zero crossing detectors 29, 30, a sign detector 31decides if the signal has a positive or a negative sign. A stream ofpositive, negative or uncertain polarity (no zero crossing or noise)signs is filtered, delayed and smoothened (blocks 32, 33) to obtain asignal as shown in FIG. 6. The resulting binary sign signal 15′ (seeFIG. 6) is used to cut out unwanted signal episodes with the use of aswitch 34. After the switch 34 the processed reference signal 10′ hasonly the signal parts of one heart activity. By cutting out the systolicor diastolic heart activity the following autocorrelation 35 has nolonger the chance for doubling.

FIG. 9 allows for a comparison of a conventionally rectified andfiltered signal and a gate-controlled signal processed according to anelement of the present disclosure.

The effect of cutting out episodes of the heart activity as discussedabove is shown in FIG. 9. A rectified and filtered signal (FIG. 9a )which is normally used for correlation has to pass a gate controlled bythe sign signal 15′. In this example signal activities having a negativesign are blocked. The result is the adjusted signal 10′ which is“doubling free”.

Here, a signal processing sequence as shown in FIG. 8 is used to avoiddouble counting. This implementation has the advantage that noadditional autocorrelation is necessary. The provided enhancementscompared with a traditional implementation include that a secondhardware channel for quadrature demodulation and zero crossing detectionand sign evaluation including filtering.

However, as the signal loses information, even though the result of theautocorrelation actually is doubling free, it might suffer loss of beatto beat accuracy.

FIG. 10 shows a signal processing according to a second element of thepresent disclosure.

In order to avoid a loss of beat to beat accuracy a preliminary fetalheart rate (uncut heart rate) is calculated element additionally using asomewhat conventional approach 40, i.e. including reference signalpreprocessing 41 followed by autocorrelation 42. In parallel a secondheart rate is calculated according the processing scheme of FIG. 8. Asecond heart rate (cut heart rate) is used to prevent the heart rateselector 43 of the first autocorrelation to wrongly take a doubled heartrate.

In a variation of the above, the second heart rate may be directlyobtained from the sign stream 15′, as it is shown in FIG. 11.

According to the element of the disclosure in FIG. 11, theautocorrelation (and postprocessing) 35′ is provided on sign stream orsignal 15′ (rather than on the cut ultrasonic echo signal 10′).

FIG. 12 shows a signal processing according to a forth element of thepresent disclosure, where the heart rate obtained from the sign streamitself is used. Provided is here additionally a sign selection 36 foreither the positive sign or the negative sign.

It is to be noted that also both signs might be used for correlation,either in combination or a course of independent evaluation of positiveand negative signs.

Corresponding elements in FIGS. 8, 10, 11 and 12 are indicated bycorresponding or similar reference signs and additional explanationthereof is therefore omitted.

FIG. 13 shows an example of a cardiotocogramm with fetal and maternalheart rate traces.

The trace snipped of a cardiotocogramm illustrated in FIG. 13 shows twotraces F, M. The upper trace F represents a fetal heart rate tracederived from an ultrasound Doppler transducer. The lower trace M showsthe maternal heart rate derived with an infrared sensor build into thetransducer measuring the uterine activity.

For this example two spatially separated independent heart rate channelsare considered. During the first half of FIG. 13, the two traces areclearly separated. There is no doubt about the correctness of therecording of the fetal heart rate. In the second half of the picture thetwo traces F, M are nearly congruent. Without the information of thematernal trace M, the fetal trace F would be interpreted as a fetaltrace, but in this example de facto the ultrasound algorithmunintentionally switched to the maternal heart rate M, which has, due tothe scoring and selection algorithm a better score than the lower scoredfetal heart rate values. A modified selection algorithm according to thepresent invention would either select the lower scored fetal heart ratefor printing or if no alternative heart rate is available suppress(blank) the printing.

The current status of printing two heart rate values (both in black,because a typically used thermoprinter does not allow color prints) isunsatisfactory, as the user has to decide which of the printed heartrates is a valid fetal heart rate, if the heart rates are nearlycongruent the overprinting blurs the fetal heart rate, and a possiblyavailable alternative heart rate is suppressed.

The cross comparison provided by here improves the reliability of afetal heart rate trace recorded with an ultrasound Doppler transducer.It reduces the likelihood of an unintended switch over to the maternalheart rate. Heart rate alterations caused by the switch over effect maymislead the trace interpretation. Misinterpreting a wrong heart ratetrace can cause unnecessary actions, unnecessary surgery, and delayeddelivery of a compromised fetus or even fetal death.

Conventional fetal monitors use ultrasound Doppler technology fornon-invasive acquisition and recording of the fetal heart rate duringgestation and labor. The mechanical contraction of the fetal heartmuscle leads to periodic signal patterns in the ultrasound reflection.The period of the patterns is used by fetal monitors to determine thefetus' current heart rate.

A major issue of this technology is its indifference for thephysiological signal source which generates the ultrasound reflection.All periodic movements of tissue or blood flow in range of the usedultrasound beam can generate a heart rate pattern. Especially pulsationsof the mother's abdominal arteries are a known cause for this problem.

The inventors realized that the different signal sources are spatiallyseparated.

An ultrasonic transducer is placed on the abdomen of a pregnant woman.During the transmission phase the piezo array is repetitively excited inorder to generate ultrasonic wave packets which are traveling towardsthe fetal heart. These traveling wave packets are reflected andfrequency shifted due to the Doppler effect on various moving layers inthe body of the pregnant women and the child for example from the fetalheart and a maternal artery. Since the fetal heart and the maternalartery are in different distances relative to the surface of thetransducer, the wave packets requires different traveling times down tothe point of reflection and back to the transducer.

The piezo element array is used in both directions. When transmissionhas finished, the transducer switches from transmit to receive mode.With only one receive window covering the entire measurement depth asignal superpositioning of a signal from a fetal signal source and amaternal source would be the result, as it is illustrated in FIG. 14.

Such a signal makes it difficult for the signal processing unit toextract the correct heart rate.

For this reason multiple receive channels are employed which are activeat different times of a measurement cycle. As already said, the echosignals from different depth require different traveling times untilthey receive the surface of the transducer. The timely staggered signalacquisition with multiple receive channels allows a proper signalseparation.

FIG. 15 illustrates a signal processing according to an embodiment ofthe invention.

FIG. 15 shows the timely hashed signal of FIG. 14 as input signals 51,52 for a respective autocorrelation 53, 54. For timely (depth)separation of the superimposed ultrasound Doppler signal discretedemodulation and filtering channels are used, but not shown here, as theskilled person is well familiar with ultrasound signal demodulation andfiltering.

The implementation method can vary depending on availability ofdemodulation and filtering paths provided by the hardware.

At least two (independent) demodulation and signal processing channelsare required to implement a basic depth splitting as provided by thisembodiment. A good implementation trade-off between signal processingpower and hardware complexity is a four channel system.

In order to keep the complexity low the description of the embodimenthere uses only two channels.

The digitized ultrasound Doppler signals are then processed in atraditional way by autocorrelation 53, 54 and post processing 55, 56 ofthe autocorrelation results. The output of each signal processing chainis a heart rate value.

Assume that first depth channel is 145 bpm (upper branch 51, 53, 55).The example further assumes that the depth range of this channel iscloser to the surface than the other which yields a heart rate of 68bpm.

In the simplified setup these two heart rate values will be availablefor comparison. The values of the ultrasound depth channels are compared58, 59 in the next step 57 with the value of the independent source 62.

The independent source used, for example, a ECG, which is subjected toprocessing 61 and determination 62 of a heart rate.

If one of the values is close to the value of the independent source thefollowing algorithm 63 can exclude this value and output 64 the fetalheart rate.

For improving the decision algorithm the depth information of theultrasound can be used to increase the accuracy for exclusion. Forexample, if the transducer is positioned traditionally with ultrasoundbeam directed versus the backbone, the heart rate calculated from thechannel with higher traveling time has the signal source farther awayfrom the surface of the transducer. If, in this example the heart ratewhich matches the value of the independent source and the depth range isbehind the layer of the other heart rate, the source of this heart rateis undoubtedly maternal. For the usual transducer positioning this isalways true, because the maternal blood vessels are spatially locatedbehind the fetal heart, but if the beam is directed from the back oreven laterally, this heuristic approach does not work.

FIG. 16 schematically shows a further element of the present disclosure.

Current fetal monitors cover a wide variety of measurable physiologicalparameters. Above all is the parameter set of fetal heart beat anduterine activity. This major pair of parameters may be supplemented byvarious maternal parameters like blood pressure, oxygen saturation,pulse and temperature.

Conventional, non-invasive methods for externally monitoring a fetus ina pregnant woman contain an Ultrasound Doppler transducer for measuringthe Fetal Heart Rate (FHR), and a pressure transducer calledtocodynamometer (Toco) for measuring uterine activity/contractions. Bothtransducers are held in place on the abdomen of the mother by an elasticbelt fitted around the waist.

The Ultrasound Doppler transducer is based on the principle that, highfrequency sound waves reflect mechanical action of the fetal heart. Themechanical contraction of the fetal heart muscle leads to periodicsignal patterns in the ultrasound reflection. The period of the patternsis used by fetal monitors to determine the fetus' current heart rate.The ultrasound transducers use arrays of piezo elements as an electromechanical converter. The array of piezo elements operatesbi-directional as transmitter and receiver. A sequencer controls thetimely switch over between transmit and receive phase. During thetransmission phase the piezo array is repetitively excited in order togenerate ultrasonic wave packets which are traveling towards the fetalheart. These traveling wave packets are reflected and frequency shifteddue to the Doppler effect on moving layers in the body of the pregnantwoman, for example at the fetal heart. While travelling down to thepoint of reflection and back to the transducer, the wave packets have topass different organic structures like, muscle tissue, fat layers oramniotic fluid. These structures have different sizes and differentdamping ratios. Fat for example has a 3 to 4 times higher absorptionfactor than water. It is obvious that large layers of fat heavilyinfluence the performance of an ultrasound transducer. In order tofacilitate the ease of monitor handling and its connected transducersthe manufacturers avoid control elements for adjustments. Thetransducers are designed to have an optimal performance on patientshaving a normal weight. With the increasing number of extremelyoverweighed and extremely underweighted patients, transducers followingthe principle “one fits all” simply exhibit a weak or bad performance ifapplied to women which do not fit to the “normal” range. Another aspectwhere transducer designed for use under normal conditions exhibit adisappointing performance is the use outside of the recommended limits.The recommended starting point for fetal heart rate examination withpulsed ultrasound Doppler is approximately the 25^(th) week ofgestation. Some countries increasingly start CTG examination at the20^(th) week of gestation and earlier. Depth placement and size of thefetal heart under this condition are significantly different compared to30^(th) week of gestation. For a sufficient registration of the fetalheart in early weeks of gestation a narrow ultrasound beam with a depthrange of sensitivity between 3 and 8 cm is normally advisable. If theearly weeks of gestation are combined with overweight the depth rangeand the ultrasound beam energy must be increased. In order to allowindividual adaptations to cover also extreme ranges of use, ultrasoundbeam energy, beam shape, range of sensitivity etc. could be madeadjustable for the user. Experienced and well trained operators may beable to use the available adjustments in a meaningful way, but astandard operator may be confused. As mentioned before adding adjustablesettings may be desirable by people doing research, but not for thestandard user. A CTG is a device which must reliably work under allconditions with a minimum level of user interaction and a minimum levelof knowledge about the mode of operation. For this reason simply addingadditional control and adjustment elements is not the way to extend therange of operation. Based on surrounding information, which is availablein many cases either in electronically stored records or as barcodes orother media the device can change its configuration automatically forthis session to achieve an optimum performance. Nowadays CTG monitorsprovide start-up menus where the input of patient data is requested. Theso called admit/discharge (ADT Admit, Discharge, Transfer) menu requestspatient demographics. The content of the patient demographics is subjectof definition. Normally patient name, week of gestation etc. arerequested on patient admittance. This information is partly displayed onthe monitor screen and printed on the paper strip. With monitorsconnected to an archiving and surveillance system the data required foradmit is retrieved from a data base and automatically loaded to themonitor if the patient is assigned to a certain bed. The extent of theADT data set is subject of free definition. In the context of thepresent invention it should preferably contain at least information onweek of gestation, BMI or alternatively height and weight, country e.g.USA or Japan, Twins, triplets (this information could also be derivedfrom the number of connected transducers).

By reading this information the monitor can categorize the data forexample the BMI in two or more groups. Based on these categories themonitor is able to configure the various parameters of the dataacquisition, signal amplification, filtering and signal processing chainindividually to achieve best CTG registration results. For example, fora patient with high BMI (=category obese) and early weeks of gestation(<25^(th) week=category premature) the monitor would adjust theultrasound beam shape to narrow, the beam intensity to high, theexpected depth range to medium/far. All this is done automatically inthe background without user interaction. Again, the possible changes foran ultrasound transducer are exemplary. For all other parameters e.g.Toco, maternal pulse the same adaptive alterations in the dataacquisition and signal processing path are possible. With theavailability of ADT data, patient aware transducer control has theadvantages of optimized signal acquisition and processing of allparameters, no or low operator interaction required, reduced exposure toenergy fields (ultrasound), no increase in the complexity of use andbeing at least in parts retrospectively applicable to the installed baseof transducers by software upgrade.

In the present context, a fetal monitor 74 with the connectedtransducers 75 is connected to a centralized surveillance and archivingsystem 72 with a data base 73. A patient is admitted to a certainmonitor or bed with a local terminal or PC 71 also connected to thesurveillance system 72. The application, running on the PC or Terminalprovides a mask 70 for patient data as a part of the admittanceprocedure. When admitting a patient the mask must be filled outcompletely. The relevant data contains the information for thetransducer 75 and signal processing control (inside 74 or 75) and isstored in the data base 20. The data set is populated to the monitor 74where the patient is assigned to. The monitor 74 may use the data forinstance if the signal processing or parts of the signal processing aredone in the monitor 74. If the signal processing is done in activetransducers 75, which may be wired or wireless, the monitor 74 makessure that the relevant information is distributed to each connectedtransducer 75. The admittance/assignment procedure ensures that the dataacquisition and signal processing procedures are automatically adaptedto the settings defined by the ADT data.

FIG. 17 schematically shows another element of the present disclosure.

In the context of this element, a near field communication path isprovided for data exchange. The near field communication device caneither be part of the monitor 74′ or a separate device connected by wireto the monitor 74′. The relevant ADT data is, together with possibleother information, stored in an individually programmed ID tag or card76. The admission process is started by bringing the tag into theproximity of the NFC device 74′. In the following step the ADT data,stored on the card 76, is read and populated to the relevant parts ofthe monitoring system 74′, 75.

In addition (or as an alternative), barcode tags containing ADT data canbe read by an attached barcode reader 77.

FIG. 18 schematically shows yet further element of the presentdisclosure.

This element uses the, in many monitors 74″, already availablepossibility for direct entry of ADT data by filling out a form sheet 78during patient admit. The data is entered manually by touch screen,keyboard or mouse is then as discussed above populated to the relevantparts of the monitor 74″ or transducer 75.

FIG. 19 schematically shows a processing device 100 in accordance withanother embodiment of the invention.

The processing device 100 includes a reference demodulation unit 101, aphase shift demodulation unit 102, a comparison unit 103 and aprocessing unit 104.

The reference demodulation unit 101, the phase shift demodulation unit102 and the comparison unit 103 are provided in duplicates,respectively, so to provide for two channels.

The reference demodulation units 101 are provided with an ultrasonicDoppler echo signal, from the respective channels, wherein eachreference demodulation unit demodulates the received echo signal usingthe carrier frequency of the ultrasonic signal used for generating theecho signal as a demodulation frequency and outputs the respectivereference demodulated signal to the comparison units 103 and to theprocessing unit 104. Similarly, the phase shift demodulation units 102,respectively, are receiving the respective ultrasonic Doppler echosignal and demodulate the echo signal using the demodulation frequency,however shifted by 90 degrees in comparison to the referencedemodulation unit, and output the phase shift demodulated signal to thecorresponding comparison unit 103.

Each comparison unit 103 is, as indicated above, provided with thereference demodulated signal and the phase shift demodulated signal forone of the channels and obtains information on a time-wise relationbetween corresponding respective signal points of the referencedemodulated signal and the phase shift demodulated signal, wherein theserespective signal points in the present embodiment are zero crossings(see FIG. 4) of the reference demodulated signal and the phase shiftdemodulated signal. As mentioned above, while the signal pointsconsidered in this context are zero crossings of the signals,nevertheless other points may be considered in the alternative or inaddition, e.g. points of maximum positive and/or negative amplitude.

The information on a time-wise relation between the respective zerocrossings for the first and second channel and the reference demodulatedsignals for the first and second channel are provided to the processingunit 104.

The processing unit 104 includes two processing sections 105, 105′, aninput section 107, a choosing section 108 and a setting unit 109. Therespective processing sections 105, 105′, one of which is provided forthe first channel, while the other one is provided for the secondchannel are provided, respectively, for three different approaches ondetermining the fetal heart rate.

According to a first approach, the information on the time-wise relationbetween the respective signal points is directly used for obtaining thefetal heart rate, as already this information includes the periodicityindicative of the fetal heart rate.

According to a second approach, the information on the time-wiserelation is used for cutting out portions of the reference demodulatedsignal, such that from such cut out demodulated signal the fetal heartrate is obtained by means of autocorrelation.

In the third approach, additionally autocorrelation is provided on thereference demodulated signal, basically according to a conventionalapproach, where the heart rate obtained by the second approach iscompared with the result and a selection section 106 of the processingsections 105, 105′ is arranged to determine the fetal heart rate byselecting either the conventionally determined heart rate or the cutheart rate.

The processing unit 104 is arranged such that for each channel therespective approach may be selected, thus providing an output for therespective channel. The input section receives external information onthe fetal heart rate to be determined or on a heart rate other than thefetal heart rate to determined, namely the maternal heart rate and isconnected to the choosing section 108. The choosing section is arrangedto select either the heart rate determined according to the firstchannel or the heart rate determined to the second channel as the fetalheart rate to be determined based on the external information.

Furthermore, as indicated above, the processing unit 104 includes asetting unit 109, wherein this setting unit is arranged to receivepatient related data and to adjust the setting of the processing unitbased on the received patient related data.

In the present embodiment the processing device 100 is provided forprocessing two separate channels, even though it is also possible thatmore than two channels are processed. Furthermore, it is also notnecessary that all three approaches discussed above are addressed in theprocessing unit, as only one or two of the discussed approaches or adifferent approach may be employed in the processing unit.

The output of the demodulation units 101 shown in FIG. 19 might besubjected to processing by an integrator and a high pass, band passfilter combination (not shown), while such elements may also be includedin the demodulation units.

FIG. 20 shows a schematic flow diagram illustrating a method fordetermining a fetal heart rate in accordance with an embodiment of theinvention.

Similar to the embodiment discussed above with respect to FIG. 19, thediscussion of FIG. 20 provides for a parallel obtaining of informationby means of two channels, even though the present invention is notlimited to this and may make use of more than two channels.

After a receiving step 200 of receiving patient related data, there isprovided an adjustment step 201, in which the setting data relevant tothe operation of the embodiment is adjusted based on the receivedpatient related data. This is followed by a channel heart ratedetermining step 202. The channel heart rate determining step 202includes determining a first heart rate from a first channel of theultrasonic Doppler echo signal and a determining of a second heart ratefrom the second channel of the echo signal. The determining of the firstheart rate includes a reference demodulation step 203, a phase shiftdemodulation step 204, a comparison step 205 and a processing step 206.Similarly, also the determining of the second heart rate includes areference demodulation step 207, a phase shift demodulation step 208, acomparison step 209 and a processing step 210.

The steps 207 to 210 basically correspond to the steps 203 to 206 andtherefore discussion is only provided for the latter.

In the reference demodulation step 203, the ultrasonic Doppler echosignal is demodulated using the carrier frequency of the ultrasonicsignal used for generating the echo signal as the demodulationfrequency, while correspondingly in the phase shift demodulation step204 the echo signal is demodulated with a shift of 90 degrees.

In the comparison step 205 the resulting reference demodulated signaland phase shift demodulated signal are compared and information on atime-wise relation between the corresponding respective signal points,which, again, are the zero crossings of the reference demodulated signaland the phase shift demodulated signal is obtained. This information isused in the processing step 206 in a process of determining the fetalheart rate.

In an input step 211, external information on the fetal heart rate isreceived, which in this case is information on the maternal heart rateobtained separately and independently. In a choosing step 212 one of theheart rates determined by use of either channel is selected as the fetalheart rate to be determined and outputted correspondingly.

FIG. 21 schematically shows a processing device 100′ in accordance withyet another embodiment of the invention in a channel mode.

The processing device 100′ includes a high frequency amplifier 110 and asplitter 111. The splitter provides the signal into a number ofsub-signals provided to the processing chains of the processing device100′. In the illustration only two chains are shown even though anyhigher number may be provided as well. Each chain includes a synchronousdemodulation unit 101′, 102′, which has a switchable demodulation clock112, 112′.

The processing device 100′ further includes a timing section 114,providing channel selection information in form of gating signals(timing signals for depth selection/measurement volume selection). Therespective gating signals are provided for gating the demodulationsignals by means of respective AND gates 115, 115′.

Each chain further includes an integration and band pass filter unit116, 116′ receiving the signal from the demodulation and providing arectified and smoothed signal to a processor 117, 117′ which is providedfor autocorrelation and heart rate evaluation.

The output of the chains is provided to a control unit 118, whichincludes an input section 107′, a choosing section 108′ and a settingsection 109′.

The input section 107′ is coupled to an external source 120 ofinformation on, for example, a maternal heart rate or depth ranges ofother ultrasound transducers or a combination of both. It is to be notedthat the external information may be also related to other heart ratesto be excluded (e.g. an independently determined fetal heart rate ofanother twin). It is even conceivable that the independently obtainedexternal information is not related to a heart rate to be disregardedbut to the fetal heart rate of interest.

The setting section 109′ is coupled to an external data base 119providing patient related data.

Similar to the embodiments discussed above, the choosing section 108′ isarranged to choose a channel (i.e. a processing chain) providing thefetal heart rate.

In the mode shown in FIG. 21, no phase shifting is provided for thedemodulation and basically each processing chain addresses a differentchannel.

FIG. 22 schematically shows the processing device 101′ of FIG. 21 in aphase-shift mode.

In contrast to the case of FIG. 21, for the demodulation unit 102′ ademodulation frequency is provided by the demodulation clock 112′, whichis shifted in phase by 90 degree in comparison to the case ofdemodulation clock 112.

Furthermore, the resulting phase shift demodulated signal is provided tothe processor 117, which compares the reference demodulated signalprovided by the demodulation unit 101′ and the phase shift demodulatedsignal so to obtain information on the time-wise relation betweencorresponding respective signal points of the reference demodulatedsignal and the phase shift demodulated signal, as it is alreadydiscussed above for other embodiments and elements of the presentdisclosure.

It is advantageous to split the volume of sensitivity covered by anultrasound Doppler sensor into several sub volumes. It is furthermoredesirable, as it becomes apparent from the present application, to avoidpossible double counting by using a quadrature demodulation in parallelto a standard synchronous demodulation. Combining both methods in onesignal processing unit with multiple channels allows reducing the numberof required channels, because the channel functionality is individuallyadaptable to different situations. At least the first part of a channel,comprising the demodulator, integrator, filtering bench and the ADconverter are until now build up in hardware. For this reason keepingthe number of channels low is not only a cost advantage. Even if in thefuture everything is done digitally, keeping the complexity of anintegrated circuit low has positive effects on power consumption, costand chip size.

As indicated above, in the illustration of FIG. 21 and FIG. 22, to keepthe example simple, only two channels are shown, even though it is to benoted that the number of channels is not limited. A suitable number ofchannels is, for example, four. As shown in FIG. 21 and FIG. 22 thereceived ultrasound signal is amplified by a high frequency amplifier110. A splitter 111 splits the signal into two to N sub signals. Eachsub signal is fed into an—in this case—identical signal processingchain. This chain starts with a synchronous demodulation unit 101′, 102′which has a switchable demodulation clock 112, 112′. The controllableswitch either selects a 0 degree phase shifted or a 90 degree phaseshifted reference clock for demodulation. The demodulation signal isfurthermore gated by use of an AND gate 115, 115′ with a gating signal.The gating signal defines the depth sensitivity, respectively volume ofsensitivity. The start point and the end point relatively to the end ofthe transmission period are freely definable for each channel. Thisallows having the volume segments either separated or overlapping. Afterdemodulation the signal is integrated, band pass filtered (elements 116,116′), rectified and smoothened in order to prepare the signal forautocorrelation in processor 117, 117′.

The control unit 118 at the end of the multiple signal processing chainsis responsible for selecting the channel which most likely measures thefetal heart rate. A reliable method for selecting a heart rate from aplurality of heart rates is to compare the heart rates with a heart ratecoming from a known source for instance derived by an ECG, as an exampleof an external source 120. Channels having similar heart rate values tothe heart rate from the known source are excluded. The excluded channelsare so to say free and do not contribute to the measurement accuracy.

This approach allows having flexible channels which can be reconfiguredin order to increase the accuracy and reliability in a case that thecontrol unit 118 realizes that a channel is in an idle state and notcontributing meaningfully. In this case the control unit 118, forexample, may set the depth range to the range of the channel which isactually measuring the fetal heart rate. It then may select the 90degree phase shift signal for demodulation to allow a quadraturedemodulation in order to obtain the direction of velocity. The sign ofthe velocity then could be used to cut out unwanted portions of thesignal to avoid double counting. If more than two channels areavailable, another channel measuring none or a wrong heart rate couldfor instance be reprogrammed in a way that this channel additionallycovers now the volume segment which was previously covered by thechannel which is now doing the quadrature demodulation. The process ofdepth volume and functionality adaptation may be either statically or adynamically controlled process done by the control unit.

Assigning the demodulation method and volume of sensitivity preferablytakes into account patient related data. For instance in early weeks ofgestation and a low BMI the algorithm would initially choose narrowvolumes of sensitivity. Initially all channels are used for depthsegmentation to find zones of activity. If the zones of activity havebeen identified the control unit 118 may change the functionality of achannel by changing for example the method of demodulation. The controlunit may also influence amplification and filtering and as a factor, therule set for extracting the heart rate out of the correlation result.Once the zones of activity are identified the control unit 118 mightdecide to put one or more channels aside the measuring channel. Theparallel working channels must not necessarily have a different methodof demodulation. Changing parameters, especially the rule set fordetermining the heart rate can result in a higher beat to beat accuracyespecially in the upper heart beat frequency ranges.

Since the health personnel is accustomed to a certain appearance of theheart rate trace print out showing traces with a higher microvariability could cause confusion and rejection. Parallel workingchannels could provide data which are different from the usual way ofpresentation. This data could be used for calculations in the backgroundto increase for example the confidence level that the ultrasoundtransducer picks up the fetal and not the maternal signal.

It should be noted that not necessarily all channels must have aswitchable demodulation source. One channel might be sufficient, eventhough, in the case that the segment with QAM channel is the measurementand sound output channel a cracking noise may be audible when themeasurement channel is moved to a different channel.

The present invention provides, among other facets, for an eliminationof double counting heart rates by cutting out unwanted signalcontributions, wherein particularly the heart rate selection may beimproved further by comparing with a second heart rate calculated onbasis of such signal with reduced information and/or by providingautocorrelation of a (binary) stream of signs indicating the phaseinformation of the ultrasonic Doppler echo signal.

Another facet of the invention provides for an exclusion of a heart ratefrom multiple heart rates derived from a depth split ultrasound Dopplersignal by comparison with a heart rate extracted from a second,independent source and/or mutual heart rate exclusion when measuringmultiple heart rate signal with multiple ultrasound Doppler sensors.

A yet further facet of the invention provides for an adaptive signalprocessing and data acquisition controlled by patient related data,allowing for optimized energy emission e.g. in case of ultrasoundtransducers, optimized operating time in case of battery powered devicesand transfer and distribution of patient related data to scatteredsignal processing and data acquisition units.

The present disclosure provides, in particular, for an ultrasoundDoppler system having multiple depth segments, wherein each depthsegment the heart rate is calculated individually and independently,while a decision unit is provided for excluding segments or heart ratevalues equal to a heart rate from a further individual or independentsource. The individual or independent heart rate source may neverthelessbe integrated into the same housing as (one of the) ultrasoundtransducers and might be for instance an IR sensor, accelerometer or thelike. Also, the individual or independent source may be located in aspatially separated, second unit (e.g. an ECG or a blood pressuremeasurement unit). Preferably, the multiple ultrasound Dopplertransducers exchange heart rate values and/or depth segments among eachother via a cable or wireless connection.

Also provided is an ultrasound Doppler system having multiple depthsegments with at least one depth segment which is supplied alternativelywith a 90 degree phase shifted demodulation signal for IQ demodulation.The phase shifted demodulation channel could be permanently set asidefor a heart rate calculation channel measuring the fetal heart rate.Further, any channel sorted out not to have a valid heart rate could beset aside a channel measuring the fetal heart rate.

According to the present disclosure, a system with multiple ultrasoundDoppler transducers measuring multiple heart rates e.g. twins ortriplets may be self-organizing in a way that heart activities measuredby one transducer are not measured by the other transducers. This couldbe done by exchanging heart rate and depth segment values with broadcastmessages or inter transducer data exchange.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality.

A single processor, device or other unit may fulfill the functions ofseveral items recited in the claims. The mere fact that certain measuresare recited in mutually different dependent claims does not indicatethat a combination of these measures cannot be used to advantage.

Operations like demodulating, comparing, (information) processing,(signal) cutting or masking, performing autocorrelation, choosing,adjusting and providing of settings, receiving and transmitting can beimplemented as program code means of a computer program and/or asdedicated hardware.

A computer program may be stored and/or distributed on a suitablemedium, such as an optical storage medium or a solid-state medium,supplied together with or as part of other hardware, but may also bedistributed in other forms, such as via the Internet or other wired orwireless telecommunication systems.

Any reference signs in the claims should not be construed as limitingthe scope.

The invention claimed is:
 1. A processing device to determine a fetalheart rate from an ultrasonic Doppler echo signal, comprising: a firstprocessing section arranged to determine a first heart rate from a firstchannel of the ultrasonic Doppler echo signal, wherein the ultrasonicDoppler echo signal comprises at least two channels, the at least twochannels including the first channel obtained for a first depth or afirst depth range and a second channel obtained for a second depth or asecond depth range different from the first depth or the first depthrange, and a second processing section arranged to determine a secondheart rate from the second channel of the ultrasonic Doppler echosignal, an input section arranged to receive, from an additional heartrate determining device, maternal heart rate information other than thedetermined first heart rate and the determined second heart rate, and achoosing section arranged to select one of the determined first heartrate and the determined second heart rate as the fetal heart rate to bedetermined based on the maternal heart rate information from theadditional heart rate determining device.
 2. The processing deviceaccording to claim 1, wherein the processing device further comprises: afirst demodulator arranged to demodulate the ultrasonic Doppler echosignal using a first channel selection information and a first inputfrequency based on a carrier frequency of an ultrasonic signal used togenerate the ultrasonic Doppler echo signal as a demodulation frequency,thus providing a first demodulated signal, and a second demodulatorarranged to demodulate the ultrasonic Doppler echo signal using a secondchannel selection information and a second input frequency based on thecarrier frequency of the ultrasonic signal used to generate theultrasonic Doppler echo signal as the demodulation frequency, thusproviding a second demodulated signal; wherein the processing device isarranged to selectively operate in one of a channel mode and aphase-shift mode; wherein, in the channel mode, the first channelselection information indicates the first channel, the second channelselection information indicates the second channel and the first andsecond input frequency are identical; and wherein, in the phase-shiftmode, the first channel selection information and the second channelselection information indicate a same channel, wherein there is a shiftof 90 degrees in phase between the first and the second input frequency,and the first demodulator and the second demodulator are to function,respectively, as a reference demodulator and a phase shift demodulator,wherein the processing device compares the first and second demodulatedsignal to obtain information on a time-wise relation; and wherein theprocessing device is arranged to switch from the channel mode to thephase-shift mode in accordance with a selection of the choosing section,wherein the first and second channel selection information indicateswhich of the first and second channel are to provide the fetal heartrate.
 3. A system to determine a fetal heart rate, comprising: anultrasonic Doppler device arranged to transmit an ultrasonic signal andto detect an ultrasonic Doppler echo signal, a processing device coupledto the ultrasonic Doppler device to receive the detected ultrasonicDoppler echo signal, wherein the processing device includes: a firstprocessing section arranged to determine a first heart rate from a firstchannel of the detected ultrasonic Doppler echo signal, a secondprocessing section arranged being arranged to determine a second heartrate from a second channel of the detected ultrasonic Doppler echosignal, wherein the first channel is obtained for a first depth or afirst depth range and the second channel is obtained for a second depthor a second depth range different from the first depth or the firstdepth range, an input section arranged to receive maternal heart rateinformation other than the determined first heart rate and thedetermined second heart rate, and a choosing section arranged to selectone of the determined first heart rate and the determined second heartrate as the fetal heart rate to be determined based on the maternalheart rate information, an additional heart rate determining devicearranged to determine an additional heart rate independently from thedetected ultrasonic Doppler echo signal, the additional heart rate beinga maternal heart rate other than the determined first heart rate and thedetermined second heart rate, and wherein the input section of theprocessing device is arranged to receive the maternal heart rate fromthe additional heart rate determining device.
 4. The system according toclaim 3, wherein the additional heart rate determining device includesone or more of: an accelerometer arranged to measure maternal heartmovements, an electrocardiograph arranged to measure maternalelectrocardiography activity, a light sensor arranged to measure lightabsorption indicative of pulsating maternal oxygen saturation, a bloodpressure sensor arranged to measure maternal blood pressure, and anadditional ultrasonic Doppler device arranged to determine theadditional heart rate.
 5. A method to determine a fetal heart rate froman ultrasonic Doppler echo signal, comprising: a channel heart ratedetermining operation of determining a first heart rate from a firstchannel of the ultrasonic Doppler echo signal and of determining asecond heart rate from a second channel of the ultrasonic Doppler echosignal, wherein the ultrasonic Doppler echo signal comprises at leasttwo channels, the at least two channels including the first channelobtained for a first depth or a first depth range and the second channelobtained for a second depth or a second depth range different from thefirst depth or the first depth range, an input operation of receiving,from an additional heart rate determining device, maternal heart rateinformation other than the determined first heart rate and thedetermined second heart rate, and a choosing operation of choosing oneof the determined first heart rate and the determined second heart rateas the fetal heart rate to be determined based on the maternal heartrate information.
 6. A non-transitory computer program product havingcomputer readable code embodied therein, when executed by one or moreprocessors, causes the one or more processors to: determine a firstheart rate from a first channel of an ultrasonic Doppler echo signal anddetermine a second heart rate from a second channel of the ultrasonicDoppler echo signal, wherein the first channel is obtained for a firstdepth or a first depth range and the second channel is obtained for asecond depth or a second depth range different from the first depth orthe first depth range, receive, from an additional heart ratedetermining device, maternal heart rate information other than thedetermined first heart rate and the determined second heart rate, andchoose one of the determined first heart rate and the determined secondheart rate as a fetal heart rate to be determined based on the maternalheart rate information from the additional heart rate determiningdevice.